Delocalization and Universality of the Fractional Quantum Hall Plateau-to-Plateau Transitions.

Disorder and electron-electron interaction play essential roles in the physics of electron systems in condensed matter. In two-dimensional, quantum Hall systems, extensive studies of disorder-induced localization have led to the emergence of a scaling picture with a single extended state, characterized by a power-law divergence of the localization length in the zero-temperature limit. Experimentally, scaling has been investigated via measuring the temperature dependence of plateau-to-plateau transitions between the integer quantum Hall states (IQHSs), yielding a critical exponent κ≃0.42. Here we report scaling measurements in the fractional quantum Hall state (FQHS) regime where interaction plays a dominant role. Our Letter is partly motivated by recent calculations, based on the composite fermion theory, that suggest identical critical exponents in both IQHS and FQHS cases to the extent that the interaction between composite fermions is negligible. The samples used in our experiments are two-dimensional electron systems confined to GaAs quantum wells of exceptionally high quality. We find that κ varies for transitions between different FQHSs observed on the flanks of Landau level filling factor ν=1/2 and has a value close to that reported for the IQHS transitions only for a limited number of transitions between high-order FQHSs with intermediate strength. We discuss possible origins of the nonuniversal κ observed in our experiments.

Initiation of atrial fibrillation by ectopic beats originating from the superior vena cava: electrophysiological characteristics and results of radiofrequency ablation.

BACKGROUND: The superior vena cava (SVC) has cardiac musculature extending from the right atrium. However, no previous study in humans has given details regarding the ectopic foci that initiate paroxysmal atrial fibrillation (PAF), which may originate from the SVC. METHODS AND RESULTS: A total of 130 patients with frequent attacks of PAF initiated by ectopic beats were included. Eight patients (6%) had spontaneous AF initiated by a burst of rapid ectopic beats from the SVC (located 19+/-7 mm above the junction of the SVC and right atrium), which was confirmed by multiplane angiographic and intracardiac echocardiographic visualization and was marked by a sharp SVC potential preceding atrial activity. During initial repetitive discharges, the group with SVC ectopy had a higher incidence of intravenous conduction block than the group with pulmonary vein ectopy (75% versus 37%; P=0.03). The activation time of the earliest intracardiac ectopic activities relative to ectopic P wave onset was significantly shorter in the SVC ectopy than the pulmonary vein ectopy group (37+/-15 versus 84+/-32 ms; P<0. 001). After 5+/-3 applications of radiofrequency energy, AF was eliminated. SVC angiography after ablation revealed a local indentation of the venous wall in one patient. Two patients manifested coexisting sinus rhythm and a "focal" fibrillating activity confined inside the SVC after radiofrequency ablation. During a follow-up period of 9+/-3 months, all 8 patients were free of antiarrhythmic drugs, without tachycardia recurrence or symptoms of SVC obstruction. CONCLUSIONS: Ectopic beats initiating PAF can originate from the SVC. A radiofrequency current delivered to eliminate these ectopies is a highly effective and safe way to prevent PAF.

Is 8-mm more effective than 4-mm tip electrode catheter for ablation of typical atrial flutter?

BACKGROUND: The prospective, randomized study comparing 4- with 8-mm tip electrodes for radiofrequency linear ablation of typical atrial flutter is not available. METHODS AND RESULTS: A total of 104 consecutive patients with typical atrial flutter were randomly assigned to undergo radiofrequency linear ablation using a 4- (Group I, n=54) or 8-mm tip electrode (Group II, n=50) catheter (temperature-control model, preset 70 degrees C). If complete bidirectional isthmus block could not be achieved after 5 pulses, the ablation catheter was changed to the other type; the maximal radiofrequency pulse number was limited to <10 pulses. Complete or incomplete isthmus conduction block was assessed by activation sequence in a multielectrode Halo catheter during low lateral right atrial and proximal coronary sinus pacing. Before shifting to the other catheter type, the 8-mm electrode catheter achieved higher complete isthmus block rate (92% versus 67%, P<0.05) with fewer pulses (2+/-1 versus 3+/-1, P<0.05), shorter procedure time (24+/-15 versus 31+/-12 minutes, P<0.05), and shorter fluoroscopic time (14+/-10 versus 23+/-15 minutes, P<0.05). After 5 failed ablation pulses, 12 (67%) of 18 patients in group I attained complete isthmus block by using an 8-mm tip catheter, but none of 4 patients in group II achieved complete block by changing to a 4-mm tip catheter. CONCLUSIONS: The 8-mm tip electrodes are more effective than the standard 4-mm length electrodes in linear ablation for typical atrial flutter. This clinical benefit may be of particular value for some patients with broad and/or thick isthmus.

Initiation of atrial fibrillation by ectopic beats originating from the pulmonary veins: electrophysiological characteristics, pharmacological responses, and effects of radiofrequency ablation.

BACKGROUND: Atrial fibrillation (AF) can be initiated by ectopic beats originating from the atrial or great venous tissues. This study investigated the anatomic characteristics and electrophysiological properties of pulmonary veins (PVs), as well as the possible mechanisms and response to drugs of ectopic foci, and assessed the effects of radiofrequency (RF) ablation on AF initiated by ectopic beats originating from PVs. METHODS AND RESULTS: Seventy-nine patients with frequent episodes of paroxysmal AF and 10 control patients were included. Distal PVs showed the shortest effective refractory periods (ERPs), and right superior PVs showed a higher incidence of intra-PV conduction block than left superior PVs. Superior and left PVs had longer myocardial sleeves than inferior and right PVs, respectively. These electrophysiological characteristics were similar between AF and control patients. Propranolol, verapamil, and procainamide suppressed ectopic beats that originated from the PVs. Of 116 ectopic foci that initiated AF, 103 (88.8%) originated from PVs. A mean of 7+/-3 RF applications completely eliminated 110 ectopic foci (94.8%). During the 6+/-2-month follow-up period, 68 patients (86. 1%) were free of AF without any antiarrhythmic drugs. Follow-up transesophageal echocardiogram showed 42.4% of ablated PVs had focal stenosis. One patient had mild exertional dyspnea after ablation, but it resolved 3 months later; 1 patient had onset of mild exertional dyspnea 5 months after ablation. CONCLUSIONS: Electrophysiological characteristics of PVs are different from those in the atria. Ectopic beats from PVs can initiate AF, and beta-adrenergic receptor blocker, calcium channel blockers, and sodium channel blockers can suppress these ectopic beats. Careful mapping and elimination of these ectopic foci can cure paroxysmal AF.

Alterations of heart rate variability after radiofrequency catheter ablation of focal atrial fibrillation originating from pulmonary veins.

BACKGROUND: Transient sinus bradycardia and hypotension have been reported as complications during radiofrequency (RF) ablation of focal atrial fibrillation (AF) originating from pulmonary veins (PVs). This study used heart rate variability (HRV) to evaluate the effects of focal PVs ablation on autonomic function. METHODS AND RESULTS: Thirty-seven patients with paroxysmal AF were referred for ablation. The study group included 30 patients who underwent transseptal ablation of PVs, and the control group included 7 patients who underwent the transseptal procedure without ablation. The mean sinus rate and time-domain (standard deviation of RR intervals and root-mean-square of differences of adjacent RR intervals) and frequency-domain (low frequency, high frequency, and low-frequency/high-frequency ratio) analyses of HRV were obtained by use of 24-hour Holter monitoring before and 1 week, 1 month, and 6 months after ablation. All the triggering points of AF were from PVs, and they were successfully ablated. Severe bradycardia and hypotension were noted during ablation of PVs in 6 patients (group IA); 24 patients without the above complication belonged to group IB. Compared with preablation values, a significant increase in mean sinus rate and low-frequency/high-frequency ratio and a significant decrease in standard deviation of RR intervals, root-mean-square of differences of adjacent RR intervals, low frequency, and high frequency were noted in groups IA and IB patients 1 week after ablation. The changes in HR and HRV recovered spontaneously in the 2 subgroups by 1 month later. These parameters of HRV did not change in the control group after the transseptal procedure. CONCLUSIONS: Transient autonomic dysfunction with alterations in HR and HRV occurred after ablation of focal AF originating from PVs.

Pulmonary vein morphology in patients with paroxysmal atrial fibrillation initiated by ectopic beats originating from the pulmonary veins: implications for catheter ablation.

BACKGROUND: Successful ablation of ectopic beats originating from the pulmonary veins (PV) could eliminate paroxysmal atrial fibrillation (PAF). However, information about the structure of the PV in patients with PAF that is initiated by PV ectopic beats has not been reported. METHODS AND RESULTS: We studied the morphology of the PVs and measured their diameters in 3 groups of patients. Group I included 52 patients (aged 66+/-14 years; 44 men) with focal atrial fibrillation (AF) from the PVs. Group II included 8 patients (aged 50+/-10 years; 3 men) with focal AF from the superior vena cava or cristal terminalis. Group III included 23 control patients (aged 55+/-16 years; 17 men). Of the control patients, 11 had AV node and 12 had AV reentrant tachycardia. After an atrial transseptal procedure, selective PV angiography using a biplane system with a right anterior oblique view of 30 degrees, a left anterior oblique view of 60 degrees, and a cranial angle of 20 degrees was performed. The ostial and proximal portions of the right and left superior PVs (RSPV and LSPV) were significantly dilated in group I patients compared with those in groups II and III. Furthermore, the ostia of the RSPV and LSPV were significantly dilated in group II compared with group III patients. However, the mean diameters of the inferior PVs were similar between the 3 groups. Comparisons of the individual PV diameters among the 3 subgroups of group I (which was divided according to where the ectopic focus was located) showed nonselective dilatation of the PV. CONCLUSIONS: Nonspecific dilatation of the ostia and proximal portion of superior PVs were found in patients with PAF initiated by ectopic beats from the superior PVs.

Effects of cavotricuspid isthmus ablation on atrioventricular node electrophysiology in patients with typical atrial flutter.

BACKGROUND: The atrial musculature in the cavotricuspid isthmus is a part of posterior inputs to the AV node. In patients with typical atrial flutter, effects of radiofrequency ablation of this isthmus on AV node conduction are still unknown. METHODS AND RESULTS: This study included 16 patients with clinically documented typical atrial flutter. Group 1 had 8 patients without and group 2 had 8 patients with dual AV nodal pathway physiology. Electrical pacing from the interatrial septum and low right atrium was performed to evaluate antegrade AV node function before and after ablation of the cavotricuspid isthmus. In group 1, the AV node conduction properties were similar before and after ablation. In group 2, the AV node Wenckebach cycle length and maximal AH interval during low right atrium (356+/-58 versus 399+/-49 ms, P=0.008; 303+/-57 versus 376+/-50 ms, P=0.008) and interatrial septum (365+/-62 versus 393+/-59 ms, P=0.008; 324+/-52 versus 390+/-60 ms, P=0.008) pacing were significantly longer after ablation. Elimination of the slow pathway after ablation was noted in 2 patients, including 1 with AV nodal reentrant echo beats. CONCLUSIONS: Radiofrequency ablation of the cavotricuspid isthmus was effective in eliminating typical atrial flutter without injury of antegrade fast AV node conduction. The atrial musculature in the cavotricuspid isthmus significantly contributed to the slow AV node conduction.

Role of autonomic tone in facilitating spontaneous onset of typical atrial flutter.

OBJECTIVES: This study sought to study the change in autonomic tone that precedes the initiation of paroxysmal atrial flutter. BACKGROUND: An abrupt change in the autonomic tone of the heart is an important initiating factor in the pathogenesis of ventricular tachyarrhythmias and paroxysmal atrial fibrillation. Whether the autonomic tone has a role in the initiation of paroxysmal atrial flutter has not been reported. METHODS: Holter electrocardiographic recording was used to investigate the changes in heart rate variability before the onset of paroxysmal atrial flutter. RESULTS: A total of 12 patients with paroxysmal atrial flutter were analyzed. An increase in the normalized value of the low frequency (LF) component and the LF/high frequency (HF) ratio and a decrease in the normalized value of the HF component began at 6 min before the onset of episodes of paroxysmal atrial flutter, which indicated that sympathovagal balance had shifted to more sympathetic predominance. CONCLUSIONS: An increase in sympathetic modulation or vagal withdrawal, or both, may facilitate the initiation of atrial flutter.

Multiple anterograde atrioventricular node pathways in patients with atrioventricular node reentrant tachycardia.

OBJECTIVES: This study sought to investigate electrophysiologic characteristics and possible anatomic sites of multiple anterograde slow atrioventricular (AV) node pathways and to compare these findings with those in dual anterograde AV node pathways. BACKGROUND: Although multiple anterograde AV node pathways have been demonstrated by the presence of multiple discontinuities in the AV node conduction curve, the role of these pathways in the initiation and maintenance of AV node reentrant tachycardia (AVNRT) is still unclear, and possible anatomic sites of these pathways have not been reported. METHODS: This study included 500 consecutive patients with AVNRT who underwent electrophysiologic study and radiofrequency ablation. Twenty-six patients (5.2%) with triple or more anterograde AV node pathways were designated as Group I (16 female, 10 male, mean age 48 +/- 14 years), and the other 474 patients (including 451 with and 23 without dual anterograde AV node pathways) were designated as Group II (257 female, 217 male; mean age 52 +/- 16 years). RESULTS: Of the 21 patients with triple anterograde AV node pathways, AVNRT was initiated through the first slow pathway only in 3, through the second slow pathway only in 8 and through the two slow pathways in 9. Of the five patients with quadruple anterograde AV node pathways, AVNRT was initiated through all three anterograde slow pathways in three and through the two slower pathways (the second and third slow pathways) in two. After radiofrequency catheter ablation, no patient had inducible AVNRT. Eleven patients (42.3%) in Group I had multiple anterograde slow pathways eliminated simultaneously at a single ablation site. Eight patients (30.7%) had these slow pathways eliminated at different ablation sites; the slow pathways with a longer conduction time were ablated more posteriorly in the Koch's triangle than those with a shorter conduction time. The remaining seven patients (27%) had a residual slow pathway after delivery of radiofrequency energy at a single or different ablation sites. The patients in Group I had a longer tachycardia cycle length, poorer retrograde conduction properties and a higher incidence of multiple types of AVNRT than those in Group II. CONCLUSIONS: Multiple anterograde AV node pathways are not rare in patients with AVNRT. However, not all of the anterograde slow pathways were involved in the initiation and maintenance of tachycardia. Radiofrequency catheter ablation was safe and effective in eliminating critical slow pathways to cure AVNRT.

Comparisons of quality of life and cardiac performance after complete atrioventricular junction ablation and atrioventricular junction modification in patients with medically refractory atrial fibrillation.

OBJECTIVES: This study compared the long-term effects of complete atrioventricular junction (AVJ) ablation with those of AVJ modification in patients with medically refractory atrial fibrillation (AF). BACKGROUND: Comparisons between the long-term effects of AVJ ablation with those of AVJ modification in patients with medically refractory AF have not been systematically studied. METHODS: Sixty patients with medically refractory AF were randomly assigned to receive complete AVJ ablation with permanent pacing or AVJ modification. Subjective perception of quality of life (QOL) was assessed by a semiquantitative questionnaire before and 1 and 6 months after ablation. Cardiac performance was evaluated by echocardiography and radionuclide angiography within 24 h (baseline) and at 1 and 6 months after ablation. RESULTS: Both methods were associated with significant improvement in general QOL and a significant reduction in the frequency of major symptoms and symptoms during attacks. The frequency of hospital admission and emergency room visits and antiarrhythmic drug trials significantly decreased after ablation in both groups. However, patients after complete AVJ ablation had a significantly greater improvement in general QOL and a significantly reduced frequency of major symptoms and symptoms during attacks (including palpitation, dizziness, chest oppression, blurred vision and syncope). Left ventricular (LV) systolic function and the ability to perform activities of daily life significantly improved after ablation in patients with depressed LV function in both groups. All improvements after ablation or modification were maintained over the 6-month follow-up period. CONCLUSIONS: AVJ ablation with permanent pacing, as compared with AVJ modification, had a significantly greater ability to decrease the frequency of attacks and the extent of symptoms of AF, and the patients who received this procedure were more satisfied with their general well-being.

Role of atrial electrophysiology and autonomic nervous system in patients with supraventricular tachycardia and paroxysmal atrial fibrillation.

OBJECTIVES: The purposes of this study were to evaluate the atrial electrophysiology and autonomic nervous system in patients who had paroxysmal supraventricular tachycardia (PSVT) associated with paroxysmal atrial fibrillation (PAF). BACKGROUND: PAF frequently appeared in patients with PSVT. However, the critical determinants for the occurrence of PAF were not clear. METHODS: This study population consisted of 50 patients who had PSVT with (n=23) and without (n=27) PAF. Atrial pressure, atrial size, atrial effective refractory periods (AERPs), and AERP dispersion were evaluated during baseline and PSVT, respectively. Twenty-four hour heart rate variability and baroreflex sensitivity (BRS) were also examined. RESULTS: There was greater baseline AERP dispersion in patients with PAF than in those without PAF. The atrial pressure, atrial size, AERPs in the right posterolateral atrium and distal coronary sinus, and AERP dispersion were increased during PSVT as compared with those during baseline. Patients with PAF had greater AERP dispersion than those without PAF during PSVT. The differences of atrial size, right posterolateral AERP, and AERP dispersion between baseline and PSVT were greater in patients with PAF than in those without PAF. BRS, but not heart rate variability, was higher in patients with PAF than in those without PAF. Univariate analysis showed that higher BRS (>4.5 ms/mm Hg, p=0.0002, odds ratio=16.1), AERP dispersion during PSVT (>40 ms, p=0.0008, odds ratio=9.7), and increase of right atrial area during PSVT (>2 cm2, p=0.016, odds ratio=10.7) were significantly correlated with the occurrence of PAF in patients with PSVT. CONCLUSIONS: Disturbed atrial electrophysiology and higher vagal reflex could play important roles in the genesis of PAF in patients with PSVT.

Prolonged fractionation of paced right atrial electrograms in patients with atrial flutter and fibrillation.

OBJECTIVES: This study investigated the extent of fractionation of paced right atrial electrograms in patients with and without paroxysmal atrial flutter (AFL) or atrial fibrillation (AF). BACKGROUND: Slow conduction through nonuniform anisotropic atrial muscles, represented by fractionated electrograms, may favor the generation of atrial tachyarrhythmias. METHODS: This study included 10 control patients (Group 1), 8 patients with documented paroxysmal AFL (Group 2) and 10 patients with documented paroxysmal AF (Group 3). Five electrode catheters were placed in the different sites of the right atrium and one catheter was positioned at the coronary sinus ostium. Atrial pacing from one site was done by a constant drive train with an extrastimulus inserted every fourth beat while recording at the other five sites was performed. The delay of each fractionated potential in the high-pass filtered atrial electrogram in response to extrastimulation was determined and used to construct conduction curves of delay versus the S1S2 interval. RESULTS: The mean increase in electrogram duration between a coupling interval of 350 ms and 10 ms above atrial refractoriness was significantly greater in Groups 2 and 3 compared with that in Group 1 (8.5 +/- 2.5 vs. 11.0 +/- 2.7 vs. 5.9 +/- 2.3 ms, respectively, p < 0.001). The mean S1S2 interval at which delay increased suddenly was also longer in Groups 2 and 3 compared with Group 1 (326 +/- 9 vs. 343 +/- 12 vs. 307 +/- 17 ms, respectively, p < 0.001). CONCLUSIONS: Increased delays in the individual potential of the fractionated atrial electrograms may be related to the development of AFL and AF.

Electrophysiologic characteristics, electropharmacologic responses and radiofrequency ablation in patients with decremental accessory pathway.

OBJECTIVES: This study sought to characterize the functional properties of decremental accessory atrioventricular (AV) pathways and to investigate their pharmacologic responses. BACKGROUND: Although decremental AV pathways associated with incessant reciprocating tachycardia have been studied extensively, information about the electrophysiologic characteristics and pharmacologic responses of anterograde and retrograde decremental AV pathways is limited. METHODS: Of 759 consecutive patients with accessory pathway-mediated tachyarrhythmia, 74 with decremental AV pathways were investigated (mean age 43 +/- 18 years). After baseline electrophysiologic study, the serial drugs adenosine, verapamil and procainamide were tested during atrial and ventricular pacing. Finally, radiofrequency catheter ablation was performed. RESULTS: Five patients had anterograde decremental conduction over the accessory pathway but had no retrograde conduction. Of the 64 patients with retrograde decremental conduction over the accessory pathway, anterograde conduction over the pathway was absent in 41 (64%), intermittent in 5 (8%) and nondecremental in 18 (28%). In the remaining five patients, anterograde and retrograde decremental conduction over the same pathway was found. The anterograde and retrograde conduction properties and extent of decrement did not differ between anterograde and retrograde decremental pathways. Posteroseptal pathways had the highest incidences of anterograde and retrograde decremental conduction. Intravenous adenosine, procainamide and verapamil caused conduction delay or block, or both, in 10 of 10, 10 of 10 and 4 of 10 of the anterograde and 20 of 20, 20 of 20 and 8 of 20 of the retrograde decremental pathways, respectively. All patients had successful ablation of the decremental pathways without complications. During the follow-up period of 31 +/- 19 months, only one patient experienced recurrence. CONCLUSIONS: Decremental accessory pathways usually had functionally distinct conduction characteristics in the anterograde and retrograde directions. Their pharmacologic responses suggested the heterogeneous mechanisms of decremental conduction.

A new electrocardiographic algorithm using retrograde P waves for differentiating atrioventricular node reentrant tachycardia from atrioventricular reciprocating tachycardia mediated by concealed accessory pathway.

OBJECTIVES: The purpose of this study was to use an electrocardiographic (ECG) algorithm, derived from the results of radiofrequency ablation, to discriminate atrioventricular node reentrant tachycardia (AVNRT) from atrioventricular reciprocating tachycardia (AVRT) and to localize a concealed accessory pathway, prospectively. BACKGROUND: Information about ECG criteria for differentiating AVNRT from AVRT is limited and has not been confirmed by surgical or catheter ablation. METHODS: Four hundred six ECGs (obtained from 406 different patients) that demonstrated narrow QRS complex (< 0.12 s) supraventricular tachycardia with an RP' interval less than the P'R interval or pseudo r' wave in lead V1 or pseudo S wave in inferior leads, or both, were examined, and the results were confirmed by radiofrequency catheter ablation. The initial 226 ECGs were analyzed to develop a stepwise algorithm, and the subsequent 180 ECGs were prospectively evaluated by the new algorithm. RESULTS: The presence of a pseudo r' wave in lead V1 or a pseudo S wave in leads II, III, aVF indicated anterior-type AVNRT with an accuracy of 100%. With the difference of RP' intervals in leads V1 and III > 20 ms, posterior-type AVNRT could be differentiated from AVRT utilizing a posteroseptal pathway with a sensitivity of 71% (95% confidence interval [CI] 55% to 89%), a specificity of 87% (95% CI 67% to 97%) and a positive predictive value of 75% (95% CI 56% to 91%). According to the polarity of retrograde P waves in leads V1, II, III, aVF and I during AVRT, the concealed accessory pathway could be localized to one of the nine regions on the atrioventricular annuli with an accuracy of 75% (for a right midseptal pathway) to 93.8% (for a left posterior pathway). Overall, the new algorithm had an accuracy of 97.8% in discriminating AVNRT from AVRT and 88.1% in localizing a concealed accessory pathway, prospectively. Prediction was incorrect in only 15 patients (9.1%). CONCLUSIONS: The new ECG algorithm derived from the analysis of retrograde P waves during tachycardia could provide a criterion for differential diagnosis between AVNRT and AVRT and for predicting the location of concealed accessory pathways.

Radiofrequency catheter ablation of common atrial flutter: comparison of electrophysiologically guided focal ablation technique and linear ablation technique.

OBJECTIVES: The purpose of this study was to study electrophysiologic characteristics and compare the electrophysiologically guided focal ablation technique and linear ablation technique in patients with common atrial flutter in a prospective randomized fashion. Background. Catheter ablation of the common atrial flutter circuit can be performed with different techniques. To date, these two techniques have not been compared prospectively in a randomized study. METHODS: Sixty patients with drug-refractory common atrial flutter were randomly assigned to undergo radiofrequency catheter ablation performed with the electrophysiologically guided focal ablation (Group I) or linear ablation technique (Group II). In Group I, radiofrequency energy was delivered to the site characterized by concealed entrainment with a short stimulus-P wave interval (<40 ms) and a postpacing interval equal to the atrial flutter cycle length. In Group II, continuous migratory application of radiofrequency energy was used to create two linear lesions in or around the inferior vena cava-tricuspid ring isthmus. Serial 24-h ambulatory electrocardiographic (Holter) and follow-up electrophysiologic studies were performed to assess recurrence of tachycardia and possible atrial arrhythmogenic effects. RESULTS: Successful elimination of the flutter circuit was achieved in 28 of 30 patients in Group I and 29 of 30 patients in Group II. More atrial premature beats and episodes of short run atrial tachyarrhythmias in the early period (within 2 weeks) after ablation were found in Group II. Recurrence rate (2 of 28 vs. 3 of 29) and incidence of new sustained atrial tachyarrhythmias (3 of 28 vs. 3 of 29) was similar in the two groups. Occurrence of recurrent atrial flutter and new sustained atrial tachyarrhythmias was related to associated cardiovascular disease and atrial enlargement in both groups. However, in Group II, the procedure time (104 +/- 17 vs. 181 +/- 29 min, p<0.01) were significantly shorter than those in Group I. CONCLUSIONS: Radiofrequency ablation of the common atrial flutter circuit was safe and effective with either the electrophysiologically guided focal ablation or linear ablation technique. However, the linear ablation technique was time-saving.

Electrophysiologic characteristics in initiation of paroxysmal atrial fibrillation from a focal area.

OBJECTIVES: We investigated the electrophysiologic characteristics in the initiation of paroxysmal atrial fibrillation (PAF) from a focal area. BACKGROUND: The electrophysiologic characteristics in the initiation of PAF are still not clear. METHODS: The study group consisted of 77 patients (M/F = 65/12, age 66 +/- 12 years) with frequent episodes of PAF; we analyzed: 1) 15 cycle lengths of electrical activity before the onset of atrial fibrillation (AF); 2) coupling interval (CI) of the first ectopic beat just before the initiation of AF; and 3) the prematurity of an ectopic beat (prematurity index [PI] = CI/mean of preceding 15 cycle lengths). RESULTS: A total of 111 episodes of sustained AF were identified. Two patterns of AF initiation were observed: group I (59/111, 53%) included the episodes preceded by cycle length oscillation, and group II (52/111, 47%) included the episodes initiated by a single ectopic beat with preceding cycle length relatively constant. The PI of group I episodes was significantly greater than that of group II (0.41 +/- 0.12 vs. 0.34 +/- 0.10, p < 0.01). The CI (267 +/- 54 ms vs. 217 +/- 55 ms, p < 0.05), AF1 (194 +/- 36 ms vs. 153 +/- 37 ms, p < 0.05) and PI (0.49 +/- 0.13 vs. 0.37 +/- 0.11, p < 0.01) of the AF episodes from the superior vena cava (SVC) were significantly longer and greater than those of AF episodes from pulmonary veins (PVs). CONCLUSIONS: In patients with PAF originating from PVs or the SVC, two major initiating patterns were found. Moreover, the electrophysiologic characteristics in the initiation of AF originating from the SVC were also different from those of AF initiating from the PVs.

Effect of phenylephrine on focal atrial fibrillation originating in the pulmonary veins and superior vena cava.

OBJECTIVES: This study was aimed at evaluating the effects of phenylephrine infusion on the occurrence of focal atrial fibrillation (AF). BACKGROUND: Paroxysmal AF can be initiated by ectopic atrial beats originating in the pulmonary vein (PV) or superior vena cava (SVC). The effect of change in autonomic tone on this focal AF is unknown. METHODS: This study included 12 patients with frequent bursts of AF documented by 24-h Holter monitoring. The number and coupling interval of spontaneous ectopic activity and bursts of AF were evaluated for 1 min before and after phenylephrine (2 to 3 microg/kg) injection. RESULTS: After detailed mapping, four patients had a focus located in the left superior PV, six in the right superior PV and two in the SVC. In 10 patients with AF foci originating in the PVs, the frequency of ectopic activity (19.5 +/- 27.4 vs. 11.4 +/- 22.9 beats/min, p = 0.059) was reduced as well as AF bursts (14 +/- 3 vs. 1.8 +/- 2.7 bursts/min, p = 0.005) before versus after phenylephrine injection; the minimal coupling interval of ectopic activity and AF bursts became longer compared with baseline. The maximal percent increase in sinus cycle length after phenylephrine injection was significantly greater in patients with complete suppression of AF compared with those with partial suppression (43 +/- 19 vs. 14 +/- 5%, p = 0.01). However, no significant effect of phenylephrine on AF originating in the SVC was found. CONCLUSIONS: Change in autonomic tone induced by phenylephrine injection was effective in suppressing focal AF originating in the PVs but not in the SVC.

Effect of high intensity drive train stimulation on dispersion of atrial refractoriness: role of autonomic nervous system.

OBJECTIVES: This study evaluated the effect of high intensity drive train (S1) stimulation on the atrial effective refractory period (ERP) and its relation to the autonomic nervous system. BACKGROUND: High intensity S1 stimulation was demonstrated to shorten the ventricular ERP and to increase dispersion of refractoriness. These effects may be due to local release of neurotransmitters. The response of the atrium and ventricle to neurotransmitters was different. The effects of high intensity S1 stimulation at the atrial tissue were evaluated. METHODS: Forty patients without structural heart disease were studied. In group 1, 20 patients, the atrial ERP was measured at 0, 7, 14, 21 and 28 mm away from the S1 site under both twice diastolic threshold and high intensity (10 mA) S1 stimulation. The same protocol was repeated after sequential administration of propranolol (0.2 mg/kg body weight) and atropine (0.04 mg/kg). In group 2, the other 20 patients, the atrial ERP was studied at three atrial sites (high lateral right atrium [HLRA], right posterior interatrial septum [RPS] and distal coronary sinus [DCS] with twice diastolic threshold and high intensity S1 stimulation at baseline and after sequential autonomic blockade. The three atrial sites were randomly assigned as the S1 location. RESULTS: In group 1, high intensity S1 stimulation shortened the atrial effective refractory period most prominently at the site of S1: (mean +/- SD) 13.3 +/- 6.4% (p < 0.001), 8.1 +/- 3.8% (p < 0.001), 4.8 +/- 4.3% (p < 0.001), 3.7 +/- 4.7% (p < 0.001) and 0.5 +/- 2.6% at 0, 7, 14, 21 and 28 mm from the S1 site, respectively. The effect of high intensity S1 stimulation was blunted with propranolol and autonomic blockade but persisted after atropine alone. High intensity S1 stimulation also increased dispersion of refractoriness (from 23 +/- 11 ms to 31 +/- 12 ms, p = 0.01), which was eliminated with autonomic blockade. In group 2, high intensity S1 stimulation had similar effects at different locations (ERP shortening of 10.8 +/- 2.7%, 10.8 +/- 2.2% and 12.2 +/- 4.6% at the HLRA, RPS and DCS, respectively). The responses to sequential autonomic blockade were similar to those in group 1. However, high intensity S1 stimulation at HLRA increased dispersion of refractoriness, but at DCS it reduced dispersion of refractoriness. CONCLUSIONS: High intensity S1 stimulation led to local shortening of the atrial ERP and increased dispersion of refractoriness. These effects were blunted with propranolol and autonomic blockade. High intensity S1 stimulation at the HLRA increased dispersion of atrial refractoriness, whereas the same stimulation at the DCS decreased dispersion of atrial refractoriness.

Reversal of atrial electrical remodeling following cardioversion of long-standing atrial fibrillation in man.

BACKGROUND: In animal studies, atrial fibrillation has been shown to shorten the atrial refractory period and impair its rate adaptation. However, little is known about the effects of chronic atrial fibrillation on atrial electrophysiology and its recovery course in humans. METHODS AND RESULTS: Nineteen patients, mean age 64 +/- 14 years, with chronic atrial fibrillation of more than six months duration were included in this study. All of them were successfully converted to sinus rhythm with an external defibrillator. Atrial effective refractory periods at right atrial appendage and distal coronary sinus were determined with five pacing cycle lengths (300, 400, 500, 600 and 700 ms) at 30 min after cardioversion and once a day for four days. The atrial conduction properties, including P wave duration of surface ECG, and right and left atrial conduction times, were also measured at the same time interval. Twenty age-matched patients without a history of atrial tachyarrhythmia were evaluated as controls. In comparison with controls, chronic atrial fibrillation significantly shortened the atrial effective refractory period, impaired its rate adaptation response, especially at distal coronary sinus, and depressed the conduction properties of atria. The atrial conduction properties did not change during the four-day follow-up period; however, the atrial effective refractory period was gradually prolonged and its rate adaptation response improved after restoration of sinus rhythm. CONCLUSIONS: In humans, chronic atrial fibrillation significantly shortened the atrial effective refractory period, and impaired its rate adaptation response. Restoration and maintenance of sinus rhythm could reverse these electrophysiological changes.

Incidence and subtypes of dementia in southern Taiwan: impact of socio-demographic factors.

OBJECTIVE: To determine the incidence rate (IR) and subtypes of dementia in southern Taiwan. METHODS: From a cohort of 2,915 community inhabitants aged 65 years and over, 2,507 and 2,175 subjects participated in the first- and second-year follow-up surveys, respectively. A two-phase study used the Mini-Mental State Examination in phase I and the Consortium to Establish a Registry of Alzheimer's Disease (CERAD) neuropsychological battery and the neurobehavioral examination in phase II. We applied International Classification of Diseases (ICD)-10NA criteria for dementia, National Institute of Neurological and Communication Disorders and Stroke-Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) guidelines for Alzheimer's disease (AD), and National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neurosciences (NINDS-AIREN) criteria for vascular dementia (VaD). RESULTS: The annual IR for total dementia was 1.28%, which increased with age from 0.77% for 65- to 74-year-olds to 6.19% for persons aged 85 years or older. AD (25 cases, 41.7%, IR=0.54%) was the most common cause of dementia, followed by VaD (19 cases, 31.7%, IR=0.41%) and mixed dementia (9 cases, 15.0%). After adjusting for sex, increasing age was significantly associated with total dementia and AD (p < 0.01). Illiteracy was associated with a marginally increased risk for total dementia (aRR=1.59, p < 0.1) as was being female for AD (aRR = 1.92, p < 0.1). The 2-year mortality rate was high among the demented (48% in total dementia, 38% in AD, and 60% in VaD). CONCLUSIONS: The age-specific incidence of dementia in Taiwan is approaching that of developed countries and the low prevalence of dementia (especially VaD) may be mainly due to the high mortality. Age was the major risk factor for total dementia and AD. Being female was probably a risk factor for AD, as was illiteracy for total dementia.